i can't seem to close the shut off valve to my upstairs cold water. the stem will not budge in either direction. this cut off valve is in a home i bought new 10 years ago and has never been used. is there anything i can do that will free up the stem so i can use this cut off valve?. would backing off the packing nut a little help? are lubricants any good to use? if i do free it up do i run the risk of the cut off valve leaking afterwards?... if all else fails should i use the main cut off valve inside my house or the one outside of my house from the main?..... THANKS.